In a related art there is a so-called split connecting rod that is manufactured by forming a semi-circular arc-shaped end portion of the connecting rod integrally with a connecting rod cap which is joined to the semi-circular arc-shaped end portion, machining a large end hole fitted to a crankpin, and then cracking and fracture-splitting, the integrally formed, piece into two pieces such as the semi-circular arc-shaped, end portion of the connecting rod and the connecting rod cap.
In this case, since joined surfaces between the semi-circular arc-shaped end portion of the connecting rod and the connecting rod cap are formed as fractured surfaces which have small concavities and convexities, it is possible to join together both surfaces in a good connection state, and it is possible to improve the quality of the connecting rod. Since it is possible to simultaneously manufacture the split semi-circular arc-shaped end portion and the connecting rod via one splitting, it is possible to reduce the manufacturing costs of the connecting rod.
However, when the fractured surface of the semi-circular arc-shaped end portion is damaged (minute projection portions of asperities become flat) in the process of inserting the piston with the connecting rod into the cylinder bore of the cylinder block, the semi-circular arc-shaped end portion may not be accurately aligned with the connecting rod cap which is joined thereto in a later step, which is a concern. Accordingly, when the split connecting rod is used, the piston is required to be inserted in such a way that none of components come into contact with the split fractured surface of the semi-circular arc-shaped end portion.
Such an insertion method in the related art is disclosed in patent literature 1. In this method, two connecting rod guides are inserted into the cylinder bore of the cylinder block before the piston with the connecting rod is inserted thereinto, the connecting rod guides are inserted into holes in both end portions of the semi-circular arc-shaped end portion of the connecting rod in such a way that end surfaces (split fractured surface) of the semi-circular arc-shaped end portion do not come into contact with the connecting rod guides, and a jig (piston pusher) for pushing the piston inward and the connecting rod guides move downward while being synchronous with each other such that the piston is inserted into the cylinder bore, and the semi-circular arc-shaped end portion of the connecting rod sits on the crankpin of the crankshaft. Since the connecting rod guides are used, while the piston is inserted into the cylinder bore, the oscillation (swing, rotation, or the like) of the connecting rod is restricted so that a fitting surface of the semi-circular arc-shaped end portion or a metal bearing can be prevented from being damaged.
A piston assembly apparatus disclosed in patent literature 2 inserts a tip end of a guide bar into a bolt hole of a large end of the connecting rod attached to the piston, and moves a tip end portion of a locking shaft inserted into a hollow portion of the guide bar, and thus the tip end of the guide bar is pushed open, the tip end of the guide bar is engaged with the bolt hole of the large end of the connecting rod, and in this state, the piston is pulled into the cylinder bore.